1. Field of the Invention
The present invention relates to a system for automatically stopping and starting an engine of a vehicle, which is designed so that when an engine-stopping condition is established during an idling operation, the engine is stopped to reduce an amount of fuel consumed, and thereafter when an engine-starting condition is established, the engine is started.
2. Description of the Prior Art
Such a system for automatically stopping and starting an engine of a vehicle is known from Japanese Patent Application Laid-open No. 10-325346. This system is designed, so that the stopping of the engine is permitted, when a quantity of power charged in a battery, i.e., a remaining capacity of the battery calculated based on the temperature, voltage and current of the battery, exceeds a sum of a quantity of power required for restarting the engine and a quantity of power required for driving auxiliaries during stoppage of the engine.
The remaining capacity of the battery is varied largely depending on the temperature of the atmosphere and the deteriorated state of the battery. For this reason, it is extremely difficult to accurately detect the remaining capacity with a small error. The above conventional system is designed to determine whether the stopping of the engine is possible, based on remaining capacity of the battery, which is difficult to accurately detect. Therefore, the conventional system is accompanied by a problem that a mis-determination is liable to occur. The conventional system also suffers from the following problem: If a condition for permitting the stopping of the engine is set severely in order to avoid the mis-determination, the stopping of the engine is prohibited even when the battery has enough energy to spare for withstanding the stoppage of the engine. Hence, an effect of sufficiently reducing the amount of fuel consumed is not provided.
The present invention has been accomplished in view of the above circumstance. It is an object of the present invention to ensure that, in a system for automatically stopping and starting an engine of a vehicle, it is possible to properly determine whether the stopping of the engine is possible, in accordance with the state of the battery.
To achieve the above object, according to one aspect of the present invention, there is provided a system for automatically stopping and starting an engine of a vehicle, which is designed so that when a stopping condition for an engine is established, the engine is stopped, and when a starting condition for the engine is then established, the engine is restarted. The system comprises a power difference calculating means for calculating a difference between a power charged in a battery in accordance with the operational state of the engine and a first consumed power brought out from the battery, a charged power integrated value calculating means for calculating an integrated value of the difference calculated by the power difference calculating means, a consumed power integrated value evaluating means for evaluating an integrated value of the first consumed power and a second consumed power brought out from the battery for a target time when the stoppage of the engine has been continued for the target time, a comparing means for comparing the integrated value calculated by the charged power integrated value calculating means with the integrated value evaluated by the consumed power integrated value evaluating means, and a determining means for determining whether the stopping of the engine is possible, based on the result of the comparison in the comparing means.
With the above arrangement, while the differences between the power charged in the battery and the consumed power brought out from the battery are integrated to calculate the integrated value of power charged in the battery, and the integrated value of power brought out from the battery when the stoppage of the engine has been continued for the target time is evaluated. When the integrated value of power charged in the battery is equal to or larger than the integrated value of power brought out from the battery during stoppage of the engine, the stopping of the engine is permitted. Therefore, it is possible to reliably prevent the restarting of the engine from being impossible due to a lack of capacity of the battery after stopping of the engine. As a result, the capacity of the battery can be suppressed to the necessary minimum, and the engine can be stopped as much as possible to preserve fuel. Particularly, the integrated value based on which it is determined whether the stopping of the engine is possible, namely, the integrated value of power actually charged in the battery, is calculated based on the difference between the charged power and the consumed power. Therefore, the accuracy of the determination can be enhanced remarkably, as compared with a system in which it is determined whether the stopping of the engine is possible, based on the remaining capacity of the battery which varies depending on various conditions such as a variation in temperature and the state of deterioration of the battery.
According to another aspect of the present invention, in addition to the arrangement described above, there is provided a system for automatically stopping and starting an engine of a vehicle wherein even if the integrated value calculated by the charged power integrated value calculating means is equal to or larger than the integrated value evaluated by the consumed power integrated value evaluating means as a result of the comparison provided by the comparing means, the engine is started when the duration of stoppage of the engine has reached the target time.
With the above arrangement, when the duration of stoppage of the engine is equal to or larger than the target time, the engine is started. Therefore, it is possible to avoid a situation in which the battery is discharged during stoppage of the engine, thereby causing the starting of the engine to be impossible. It is also possible to avoid a situation in which the battery is deteriorated due to its secular change, thereby causing the starting of the engine to be impossible.